Process for the crystallization of ddt



March 25, 1952 J. KALLOK 2,590,544

PROCESS FOR THE CRYSTALLIZATION OF DDT FildApril 19, 1949 Mo/fen 0. D. 7?

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John L. kaflok Patented Mar. 25, 1952 john Kal l ok; f iq f ance, fialifq assigfior to:- Mcntfiose Gheinical, Corporation. t California,

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le's', Calit., a cbtbcration of; Delaware Application sprin s, 1949, Serial no. 88,4 89

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h s nvention relates; to an mprovem nt. n we ma f c ure ch ore iphenyl; trich omr eth ne i ma r alis widelru'sed. as. ins secticide, its so-called para-para isomer (2.2 b (p -chl(; rophenyl) 1 ;,l,1 trichloroethane), haw j unique properties in thisrespect. The-malterial ispmducedjas a mixtureof-seyeral isomers n y hem st ommonly mp cyedformisknd'wn asft'echnical DDT." This, is a solid material; at rdinarytemperatures, but, melts readily atjhe low 100 (1., usually at about 90 C. The efiecztive. in redient in the DDT, the so-called parapara isomer, melts at about 106 C.

For convenience and simplicity in expression, dichlorodiphenyl trichloroethane will be referred to hereinafter as DDT.

To employ DDT as an insecticide it is usual to place it in solution or else to sub-divide it to finely, divided form anddisperse it in a. dust;- like; carrier. Since DDT exhibits mahyjchar; acteristics which can be compared to those of sugar or sucrose in that if av DDT solution is cooled it,v forms, a liquid mass comparable to molasses and whichsolidifiesonly after passage of such an extremely long period of time as to be uneconomical in commercial practice; even wherifsolidified the materialmay be gummyand" sticky and is difiicult to grind. It has beensiig: gested that DDT solutions should be cooled to a temperature not above about 60 C., without solidification, to produce a supercooled liquid, the latter being set aside and permitted to crystallize; the rate of cooling is sufficient to avoid crystallization during the cooling operation, it being essential to produce a supercooled liquid. This practice, I have found, is not feasible in commercial operation because of the tendency to produce a molasses-like material in which the DDT forms a solid so slowly as to be uneconomical iri commercial practice, the solidification requiring a matter of weeks. The other commercial practices used at present are such as to make the cooling operation extremely difiicult and expensive and to give a final product containing gummy constituents which make the solid dimcult and expensive to grind, and which prevent the material from being free-flowing and noncaking.

I have found that if one cools the DDT solution under such conditions that a minimum of supercooling is effected and so that many fine other suitable comminution methods. More particularly, I, have found that DDT should be cooledin film form and under such conditions that it. worked with great vigor during the cooling operation. If this is done, then a hard productr'esultsas compared to one which has the molasses-like properties which characterizes the productproducedwith super-cooling of liquid DDT.

The invention is conveniently practiced by feeding thelliquified DDT onto the first of aplurality of rollers, the severairollers being set so closely tcg'thtaithat a minimum thicknessfilm is carfried upon each roll; the respectiverolls arecooled toa temperatureapproximating a normal atmospherictemperature, that is, preferably below. C., andlprefe'r'ably between 5 and. 30 C; and usually about 10 C. Crystallization can be carried on continuously, the DDT being fed onto one roll and'cut oif the final roll of the series. The. rolls are'preferably diiferentially driven so that the DDTfilm on any given roll is torn apart and worked vigorously by the roll which rotates substantially in contact with it. Differential driving is not necessaryif the rolls are so s'etwith respectto one another as to effect a. squeezing, together and a pulling apart of the.

material. In this manner, millions of fine crystal nuclei are formed fractially instantaneously in the freshly fed and filmed DDT liquid. The vigorous working carried these fine crystal nuclei to all parts of the liquid film while it undergoes cooling so that crystallization takes place with crystal nuclii are formed in the mass, then a solid DDT is produced which is hard, and is free of gummy constituents and which can be readily reduced to a finely divided form by grinding or great rapidity and a solid, hard mass results.

The invention will be further illustrated by the following examples, but is not limited to these in the drawing accompanying and forming a part hereof, Figures 1 and 2 are diagrammatic representations of the apparatus utilized respectively in Examples 1 and 2, as follows:

Example 1.--Two 8 rolls, indicated at 6 and I in Figure 1 of the drawing, were driven respectively at 20 R. P. M. and 25 R. P. M. DDT was fed as at 8 onto the first roll 6 to cover the roll completely and to provide a slight excess to work in and fill the bite between the rolls. After av few minutes operation, the DDT liquid coating on the rolls began to crystallize and as soon as crystallization was complete, the solid DDT was removed continuously with a doctor knife 9 as brittle chunks from the final roll 1.

Example 2.To illustrate further the practice of the present invention, a five-roll device was set up as in Figure 2, including rolls 2|, 22, 23, 24 and 25. Molten DDT at to C. was fed onto roll 2| from feeder 26 and onto roll 23 from feeder 21. A doctor knife 28 was so positioned with respect to roll 2| that the material out therefrom dropped onto roll 23. Similarly, a doctor knife 29 was so positioned that material out from roll 22 dropped between rolls 23 and 24. The material from roll 2| which was still liquid but cool, was cut off by the knife 28 and dropped onto roll 23, as indicated at 33. The material transferred to roll 22 was also out off by doctor knife 29 and fell into the bite between rolls 23 and 24, as indicated at 32. The material from roll 22 was partially crystallized and, by the time it had transferred from between roll 23 and 24 and between rolls 24 and 25, crystallization was complete. The DDT was cut off the final roll 25 by knife 3i at the rate of 1,000 pounds per hour and was dry and brittle.

The condition of the DDT on each roll, its temperature and speed of rotation are given in the following table:

To produce a relatively soft, flaky DDT which can be ground easily, the molten DD I' is agitated violently in a water cooled vessel to about 75 C. During the cooling, DDT crystals are formed and are broken up by the violent agitation so that a partially crystallized, mushy mixture is formed. This mushy mixture is then fed onto the multiple chilled rolls, as in Example 2. The product is softer than that produced when the molten DDT is fed directly to the rolls, but it is still flaky and is particularly suited for grinding in certain types of mills.

I claim:

1. The process of solidifying DDT to a hard crystalline form which consists essentially in continuously cooling molten DDT in the form of a film from a temperature above its setting point to a final temperature between 5 C. and 30 C., to effect, initially, formation of a multitude of crystal nuclei in the liquid and, finally, formation of a firm solid and, simultaneously and continuously during such continuous cooling, working the DDT in the form of a film until the DDT attains said final temperature and is of a hard crystalline form.

2. The process of solidifying DDT to a hard crystalline form which consists essentially in continuously cooling molten DDT in the form of a film from .a temperature above its setting point to a final temperature of about 10 C. to effect, initially, formation of a multitude of crystal nuclei in the liquid and, finally, formation of a firm solid and, simultaneously and continuously during such continuous cooling, working the .DDT in the form of a film until the DDT attains said final temperature and is of a hard crystalline form.

3. The process of solidifying DDT to a hard crystalline form which consists essentially in first cooling a mass of molten DDT from a temperature above its setting point to about C. while violently agitating the mass to produce a mushy mixture, and then cooling the mushy mixture continuously in the form of a film from said temperature of about 75 C. to 30 C. and during such continuous cooling working the DDT continuously as a film until the film is a solid and the DDT is at a final temperature between 5 C. and 30 C'.

JOHN L. KALLOK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,883,112 Tiers Oct. 18, 1932 2,200,774 Halliday May 14, 1940 2,453,076 Little Nov. 2, 1948 2,491,160 Bruce Dec. 13, 1949 2,555,309 Beam June 5, 1951 FOREIGN PATENTS Number Country Date 455,683 Germany Feb. 6, 1928 

1. THE PROCESS OF SOLIDIFYING DDT TO A HARD CRYSTALLINE FORM WHICH CONSISTS ESSENTIALLY IN CONTINUOUSLY COOLING MOLTEN DDT IN THE FORM OF A FILM FROM A TEMPERATURE ABOVE ITS SETTING POINT TO A FINAL TEMPERATURE BETWEEN 5* C. AND 30* C., TO EFFECT, INITIALLY, FORMATION OF A MULTITUDE OF CRYSTAL NUCLEI IN THE LIQUID AND, FINALLY FORMATION OF A FIRM AND, SIMULTANEOUSLY AND CONTINUOUSLY DURING SUCH CONTINUOUS COOLING, WORKING THE DDT IN THE FORM OF A FILM UNTIL THE DDT ATTAINS SAID FINAL TEMPERATURE AND IS OF A HARD CRYSTALLINE FORM. 